netdev - Re: [PATCH net-next v4 1/3] net: ipv6: Unduplicate {raw,udp}v6

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Date:	Thu, 24 Apr 2014 17:43:05 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Lorenzo Colitti <lorenzo@...gle.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next v4 1/3] net: ipv6: Unduplicate {raw,udp}v6_sendmsg code

On Fri, Apr 25, 2014 at 12:13:57AM +0900, Lorenzo Colitti wrote:
> On Fri, Apr 25, 2014 at 12:02 AM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> > > I am afraid we could jump to do_append_data without having dontfrag
> > > initialized. The jump happens before we call to ip6_datagram_send_common.
> > >
> > > So the initialization of dontfrag to -1 needs to be added to the caller.
> >
> > Also see e36d3ff91130002 (udp6: respect IPV6_DONTFRAG sockopt in case there
> > are pending frames) which was a bug we had some time ago.
> 
> Hmm. So I'm the second person to trip over that goto. It doesn't help
> that the compiler didn't notice that it could have been used
> uninitialized.
> 
> I wonder, is it better to just initialize dontfrag to np->dontfrag
> instead of -1 in the caller? ip6_datagram_send_ctl seems to just
> overwrite dontfrag with whatever comes from userspace, so nobody ever
> checks that it's < 0.

Yes, that is what I had in mind. So we must not reset dontfrag to -1 in
datagram_common_send and leave the check just after do_append_data as is.

Bye,

  Hannes

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